GDB调试--多线程

一. GDB与多线程

在多线程编程时，当我们需要调试时，有时需要控制某些线程停在断点，有些线程继续执行。有时需要控制线程的运行顺序。有时需要中断某个线程，切换到其他线程。这些都可以通过gdb实现。GDB默认支持调试多线程，跟主线程，子线程block在create+thread。

先来看一下gdb调试多线程常用命令：

info+threads：显示可以调试的所有线程。gdb会为每个线程分配一个ID（和tid不同），编号一般从1开始。后面的ID是指这个ID。

thread+ID：切换当前调试的线程为指定ID的线程。

(gdb) help set scheduler-lockingSet mode for locking scheduler during execution.off  == no locking (threads may preempt at any time)on   == full locking (no thread except the current thread may run)step == scheduler locked during every single-step operation.        In this mode, no other thread may run during a step command.        Other threads may run while stepping over a function call ('next')

#include<stdio.h>#include<pthread.h>void *thread_run1(void *argv){    printf("I am thread_run1, thread_run1:%u\n", pthread_self());    return NULL;}void *thread_run2(void *argv){    printf("I am thread_run2, thread_run2:%u\n", pthread_self());    return NULL;}int main(int argc, char *argv[]){    pthread_t pid1, pid2;    pthread_create(&pid1, NULL, thread_run1, NULL);    pthread_create(&pid2, NULL, thread_run2, NULL);    pthread_join(pid1, NULL);    pthread_join(pid2, NULL);    return 0;}

cfc:/app/tmp>gdb somethreadGNU gdb (GDB) Red Hat Enterprise Linux (7.2-90.el6)Copyright (C) 2010 Free Software Foundation, Inc.License GPLv3+: GNU GPL version 3 or later <http://gnu.org/licenses/gpl.html>This is free software: you are free to change and redistribute it.There is NO WARRANTY, to the extent permitted by law.  Type "show copying"and "show warranty" for details.This GDB was configured as "x86_64-redhat-linux-gnu".For bug reporting instructions, please see:<http://www.gnu.org/software/gdb/bugs/>...Reading symbols from /app/tmp/somethread...done.(gdb) break thread_run1Breakpoint 1 at 0x400620: file somethread.c, line 6.(gdb) break thread_run2Breakpoint 2 at 0x400650: file somethread.c, line 12.(gdb) info bNum     Type           Disp Enb Address            What1       breakpoint     keep y   0x0000000000400620 in thread_run1 at somethread.c:62       breakpoint     keep y   0x0000000000400650 in thread_run2 at somethread.c:12(gdb) runStarting program: /app/tmp/somethread [Thread debugging using libthread_db enabled][New Thread 0x7ffff7fe5700 (LWP 17196)][Switching to Thread 0x7ffff7fe5700 (LWP 17196)]Breakpoint 1, thread_run1 (argv=0x0) at somethread.c:66               printf("I am thread_run1, thread_run1:%u\n", pthread_self());Missing separate debuginfos, use: debuginfo-install glibc-2.12-1.192.el6.x86_64(gdb) info threads[New Thread 0x7ffff75e4700 (LWP 17197)]  3 Thread 0x7ffff75e4700 (LWP 17197)  0x0000003d8a2e8a71 in clone () from /lib64/libc.so.6* 2 Thread 0x7ffff7fe5700 (LWP 17196)  thread_run1 (argv=0x0) at somethread.c:6  1 Thread 0x7ffff7fe7700 (LWP 17193)  0x0000003d8a2e8a71 in clone () from /lib64/libc.so.6(gdb) cContinuing.I am thread_run1, thread_run1:4160640768[Thread 0x7ffff7fe5700 (LWP 17196) exited][Switching to Thread 0x7ffff75e4700 (LWP 17197)]Breakpoint 2, thread_run2 (argv=0x0) at somethread.c:1212              printf("I am thread_run2, thread_run2:%u\n", pthread_self());(gdb) info threads* 3 Thread 0x7ffff75e4700 (LWP 17197)  thread_run2 (argv=0x0) at somethread.c:12  1 Thread 0x7ffff7fe7700 (LWP 17193)  0x0000003d8a6082fd in pthread_join () from /lib64/libpthread.so.0(gdb) nI am thread_run2, thread_run2:415015091213              return NULL;(gdb) n14      }(gdb) n0x0000003d8a607aa1 in start_thread () from /lib64/libpthread.so.0(gdb) info threads* 3 Thread 0x7ffff75e4700 (LWP 17197)  0x0000003d8a607aa1 in start_thread () from /lib64/libpthread.so.0  1 Thread 0x7ffff7fe7700 (LWP 17193)  0x0000003d8a6082fd in pthread_join () from /lib64/libpthread.so.0(gdb) nSingle stepping until exit from function start_thread,which has no line number information.[Thread 0x7ffff75e4700 (LWP 17197) exited]Program received signal SIGSTOP, Stopped (signal).[Switching to Thread 0x7ffff7fe7700 (LWP 17193)]0x0000003d8a6082fd in pthread_join () from /lib64/libpthread.so.0(gdb) nSingle stepping until exit from function pthread_join,which has no line number information.main (argc=1, argv=0x7fffffffdd88) at somethread.c:2424              return 0;(gdb) n25      }(gdb) n0x0000003d8a21ed1d in __libc_start_main () from /lib64/libc.so.6(gdb) nSingle stepping until exit from function __libc_start_main,which has no line number information.Program exited normally.(gdb) info threads(gdb) runStarting program: /app/tmp/somethread [Thread debugging using libthread_db enabled][New Thread 0x7ffff7fe5700 (LWP 17199)][Switching to Thread 0x7ffff7fe5700 (LWP 17199)]Breakpoint 1, thread_run1 (argv=0x0) at somethread.c:66               printf("I am thread_run1, thread_run1:%u\n", pthread_self());(gdb) info threads[New Thread 0x7ffff75e4700 (LWP 17200)]  3 Thread 0x7ffff75e4700 (LWP 17200)  0x0000003d8a2e8a71 in clone () from /lib64/libc.so.6* 2 Thread 0x7ffff7fe5700 (LWP 17199)  thread_run1 (argv=0x0) at somethread.c:6  1 Thread 0x7ffff7fe7700 (LWP 17198)  0x0000003d8a2e8a71 in clone () from /lib64/libc.so.6(gdb) n[Switching to Thread 0x7ffff75e4700 (LWP 17200)]Breakpoint 2, thread_run2 (argv=0x0) at somethread.c:1212              printf("I am thread_run2, thread_run2:%u\n", pthread_self());(gdb) info threads* 3 Thread 0x7ffff75e4700 (LWP 17200)  thread_run2 (argv=0x0) at somethread.c:12  2 Thread 0x7ffff7fe5700 (LWP 17199)  0x00000000004004d8 in printf@plt ()  1 Thread 0x7ffff7fe7700 (LWP 17198)  0x0000003d8a6082fd in pthread_join () from /lib64/libpthread.so.0(gdb) nI am thread_run1, thread_run1:4160640768I am thread_run2, thread_run2:415015091213              return NULL;(gdb) info threads* 3 Thread 0x7ffff75e4700 (LWP 17200)  thread_run2 (argv=0x0) at somethread.c:13  2 Thread 0x7ffff7fe5700 (LWP 17199)  0x0000003d8a605e20 in __nptl_death_event () from /lib64/libpthread.so.0  1 Thread 0x7ffff7fe7700 (LWP 17198)  0x0000003d8a6082fd in pthread_join () from /lib64/libpthread.so.0(gdb) n14      }(gdb) n0x0000003d8a607aa1 in start_thread () from /lib64/libpthread.so.0(gdb) info threads* 3 Thread 0x7ffff75e4700 (LWP 17200)  0x0000003d8a607aa1 in start_thread () from /lib64/libpthread.so.0  2 Thread 0x7ffff7fe5700 (LWP 17199)  0x0000003d8a605e20 in __nptl_death_event () from /lib64/libpthread.so.0  1 Thread 0x7ffff7fe7700 (LWP 17198)  0x0000003d8a6082fd in pthread_join () from /lib64/libpthread.so.0(gdb) killKill the program being debugged? (y or n) y(gdb) runStarting program: /app/tmp/somethread [Thread debugging using libthread_db enabled][New Thread 0x7ffff7fe5700 (LWP 17202)][Switching to Thread 0x7ffff7fe5700 (LWP 17202)]Breakpoint 1, thread_run1 (argv=0x0) at somethread.c:66               printf("I am thread_run1, thread_run1:%u\n", pthread_self());(gdb) info threads[New Thread 0x7ffff75e4700 (LWP 17203)]  3 Thread 0x7ffff75e4700 (LWP 17203)  0x0000003d8a60e2fe in __lll_lock_wait_private () from /lib64/libpthread.so.0* 2 Thread 0x7ffff7fe5700 (LWP 17202)  thread_run1 (argv=0x0) at somethread.c:6  1 Thread 0x7ffff7fe7700 (LWP 17201)  0x0000003d8a2e8a71 in clone () from /lib64/libc.so.6(gdb) sI am thread_run1, thread_run1:41606407687               return NULL;(gdb) info threads  3 Thread 0x7ffff75e4700 (LWP 17203)  0x0000003d8a60e48f in __lll_unlock_wake_private () from /lib64/libpthread.so.0* 2 Thread 0x7ffff7fe5700 (LWP 17202)  thread_run1 (argv=0x0) at somethread.c:7  1 Thread 0x7ffff7fe7700 (LWP 17201)  0x0000003d8a6082fd in pthread_join () from /lib64/libpthread.so.0(gdb) n8       }(gdb) info threads  3 Thread 0x7ffff75e4700 (LWP 17203)  0x0000003d8a60e48f in __lll_unlock_wake_private () from /lib64/libpthread.so.0* 2 Thread 0x7ffff7fe5700 (LWP 17202)  thread_run1 (argv=0x0) at somethread.c:8  1 Thread 0x7ffff7fe7700 (LWP 17201)  0x0000003d8a6082fd in pthread_join () from /lib64/libpthread.so.0(gdb) cContinuing.[Switching to Thread 0x7ffff75e4700 (LWP 17203)]Breakpoint 2, thread_run2 (argv=0x0) at somethread.c:1212              printf("I am thread_run2, thread_run2:%u\n", pthread_self());(gdb) info threads* 3 Thread 0x7ffff75e4700 (LWP 17203)  thread_run2 (argv=0x0) at somethread.c:12  2 Thread 0x7ffff7fe5700 (LWP 17202)  thread_run1 (argv=0x0) at somethread.c:8  1 Thread 0x7ffff7fe7700 (LWP 17201)  0x0000003d8a6082fd in pthread_join () from /lib64/libpthread.so.0(gdb) sI am thread_run2, thread_run2:415015091213              return NULL;(gdb) s14      }(gdb) n0x0000003d8a607aa1 in start_thread () from /lib64/libpthread.so.0(gdb) nSingle stepping until exit from function start_thread,which has no line number information.[Thread 0x7ffff75e4700 (LWP 17203) exited]Program received signal SIGSTOP, Stopped (signal).[Switching to Thread 0x7ffff7fe7700 (LWP 17201)]0x0000003d8a6082fd in pthread_join () from /lib64/libpthread.so.0(gdb) nSingle stepping until exit from function pthread_join,which has no line number information.nnn^CProgram received signal SIGINT, Interrupt.0x0000003d8a6082fd in pthread_join () from /lib64/libpthread.so.0(gdb) info threads  2 Thread 0x7ffff7fe5700 (LWP 17202)  0x0000003d8a605e20 in __nptl_death_event () from /lib64/libpthread.so.0* 1 Thread 0x7ffff7fe7700 (LWP 17201)  0x0000003d8a6082fd in pthread_join () from /lib64/libpthread.so.0(gdb) 

二、设置core

     core的意思是核心，dumped的意思就是抛出，转储，core  dumped就是核心转储的意思。当一个进程异常退出前，该进程会抛出当时该程序进程的内存详细情况存储在硬盘上，文件名通常是core，这就叫core  dump。

进程异常终止通常是因为代码存在BUG，比如非法内存访问导致段错误，事后可以用调试器检查core文件以查清错误原因，这叫做事后调试.

uname  -a   查看机器参数

ulimit  -a   查看默认参数

ulimit   -c   1024     设置core文件大小为1024

ulimit  -c   unlimit   设置core文件大小为无限

eg1（可以快速定位出问题的位置）

gdb  a.out  core.xxx

where

eg2    (在  gdb  中使用) 

（gdb） core-file  core.xxx